Laure Guerrini

Population Structuring of Glossina palpalis gambiensis (Diptera: Glossinidae) According to Landscape Fragmentation in the Mouhoun River, Burkina Faso

Abstract The impact of landscape fragmentation due to human and climatic mediated factors on the structure of a population of Glossina palpalis gambiensis Vanderplank (Diptera: Glossinidae) was investigated in the Mouhoun river basin, Burkina Faso. Allele frequencies at five microsatellite loci, and metric properties based on 11 wing landmarks, were compared between four populations. The populations originated from the Mouhoun river and one of its tributaries. The average distance between samples was 72 km with the two most widely spaced populations being 216 km apart. The sampling points traversed an ecological cline in terms of rainfall and riverine forest ecotype, along a river enlarging from downstream to upstream and oriented south to north. Microsatellite DNA comparison demonstrated structuring between the populations, but not complete isolation, with an overall Fst = 0.012 (P < 0.001). Wing geometry revealed significant centroid size and shape differences between populations, especially between the two most distant populations. There was no significant correlation between gene flow and geographic distance at this scale, but there was a positive correlation in females between metric distances (wing shape differences) and geographic distances that might be attributed to the cline of environmental conditions. The impact of the fragmentation of riparian landscapes on tsetse population structure is discussed in the context of control campaigns currently promoted by Pan African Tsetse and Trypanosomosis Eradication Campaign.

A phyto-sociological analysis of the distribution of riverine tsetse flies in Burkina Faso.

Abstract.  In Burkina Faso, Glossina palpalis gambiensis Vanderplank and G. tachinoides Westwood (Diptera: Glossinidae) are the main cyclic vectors of trypanosomiasis. The vegetation type along river banks is an important factor determining the distribution and abundance of these tsetse. The following work investigated the relation between the plant species present (including the disturbance level) and tsetse distribution and abundance, using three ecotypes, described by P.C. Morel in 1978. These were the Guinean, Sudano‐Guinean and Sudanese gallery forests. In the Mouhoun River basin, these three ecotypes are found successively from upstream to downstream. Berlinia grandiflora, Syzygium guineense and Cola laurifolia and finally Acacia seyal and Mitragyna inermis were the best indicators for the Guinean, Sudano‐Guinean and Sudanese gallery forest ecotypes, respectively, as suggested by Morel. However, other species such as Pterocarpus santalinoides and Mimosa pigra were not ecotype specific. Trap catches confirmed that G. palpalis and G. tachinoides are predominant in Guinean and Sudanese gallery forests, respectively, and that both species are well represented in the Sudano‐Guinean ecotype. Tsetse densities dropped significantly in disturbed Sudano‐Guinean and Sudanese gallery forest sites. However, this was not the case for both species in Guinean or for G. tachinoides in half‐disturbed Sudanese gallery forest sites, confirming their high resilience to human‐made changes. The importance of a detailed consideration of riverine ecotypes when predicting tsetse densities is discussed.

Stratified Entomological Sampling in Preparation for an Area-Wide Integrated Pest Management Program: The Example of Glossina palpalis gambiensis (Diptera: Glossinidae) in the Niayes of Senegal

ABSTRACT The riverine tsetse species Glossina palpalis gambiensis Vanderplank 1949 (Diptera: Glossinidae) inhabits riparian forests along river systems in West Africa. The government of Senegal has embarked on a project to eliminate this tsetse species, and African animal trypanosomoses, from the Niayes area using an area-wide integrated pest management approach. A stratified entomological sampling strategy was therefore developed using spatial analytical tools and mathematical modeling. A preliminary phytosociological census identified eight types of suitable habitat, which could be discriminated from LandSat 7 ETM+ satellite images and denominated wet areas. At the end of March 2009, 683 unbaited Vavoua traps had been deployed, and the observed infested area in the Niayes was 525 km2. In the remaining area, a mathematical model was used to assess the risk that flies were present despite a sequence of zero catches. The analysis showed that this risk was above 0.05 in 19% of this area that will be considered as infested during the control operations. The remote sensing analysis that identified the wet areas allowed a restriction of the area to be surveyed to 4% of the total surface area (7,150 km2), whereas the mathematical model provided an efficient method to improve the accuracy and the robustness of the sampling protocol. The final size of the control area will be decided based on the entomological collection data. This entomological sampling procedure might be used for other vector or pest control scenarios.

Fragmentation Analysis for Prediction of Suitable Habitat for Vectors: Example of Riverine Tsetse Flies in Burkina Faso

Abstract Tsetse flies are the cyclic vectors of sleeping sickness and African animal trypanosomosis. The possibility to classify the natural habitat of riverine tsetse species is explored in the Mouhoun River basin, Burkina Faso: the objectives were to discriminate the riverine forests community types and their fragmentation levels by using Landsat 7 enhanced thematic mapper images, to map tsetse densities. Glossina palpalis gambiensis Vanderplank 1949 (Diptera: Glossinidae) and G. tachinoides Westwood, 1850 are the vectors of trypanosomoses in this area. After a supervised classification, the community types were discriminated using the water area in 400-m-wide polygons around the river. A fragmentation analysis of the swamp forest unit, cross-tabulated with the community types, lead to identification of the final landscapes where tsetse apparent densities (ADT) were implemented using a training data set of 608 trap locations. The predicted ADT were then compared with an independent validation data set of 78 trap locations. The correlation between the model predictions and the validation data set was high, validating this approach (P < 0.001). The riverine forest community type and fragmentation level are critical factors for riverine tsetse species, which should be taken into consideration to map their suitable habitat.

Population structure of Glossina palpalis gambiensis (Diptera: Glossinidae) between river basins in Burkina Faso: Consequences for area-wide integrated pest management

African animal trypanosomosis is a major obstacle to the development of more efficient and sustainable livestock production systems in West Africa. Riverine tsetse species such as Glossina palpalis gambiensis Vanderplank are their major vectors. A wide variety of control tactics is available to manage these vectors, but their elimination will only be sustainable if control is exercised following area-wide integrated pest management (AW-IPM) principles, i.e. the control effort is targeting an entire tsetse population within a circumscribed area. In the present study, genetic variation at microsatellite DNA loci was used to examine the population structure of G. p. gambiensis inhabiting two adjacent river basins, i.e. the Comoé and the Mouhoun River basins in Burkina Faso. A remote sensing analysis revealed that the woodland savannah habitats between the river basins have remained unchanged during the last two decades. In addition, genetic variation was studied in two populations that were separated by a man-made lake originating from a dam built in 1991 on the Comoé. Low genetic differentiation was observed between the samples from the Mouhoun and the Comoé River basins and no differentiation was found between the samples separated by the dam. The data presented indicate that the overall genetic differentiation of G. p. gambiensis populations inhabiting two adjacent river basins in Burkina Faso is low (F(ST)=0.016). The results of this study suggest that either G. p. gambiensis populations from the Mouhoun are not isolated from those of the Comoé, or that the isolation is too recent to be detected. If elimination of the G. p. gambiensis population from the Mouhoun River basin is the selected control strategy, re-invasion from adjacent river basins may need to be prevented by establishing a buffer zone between the Mouhoun and the other river basin(s).

Population structuring of the tsetse Glossina tachinoides resulting from landscape fragmentation in the Mouhoun River basin, Burkina Faso

The impact of landscape fragmentation resulting from human‐ and climate‐mediated factors on the structure of a population of Glossina tachinoides Westwood (Diptera: Glossinidae) in the Mouhoun River basin, Burkina Faso, was investigated. Allele frequencies at five microsatellite loci were compared in four populations. The average distance between samples was 72 km. The sampling points traversed an ecological cline in terms of rainfall and riverine forest ecotype, along a river loop that enlarged from upstream to downstream. Microsatellite DNA demonstrated no structuring among the groups studied (FST = 0.015, P = 0.07), which is contrary to findings pertaining to Glossina palpalis gambiensis Vanderplank in the same geographical area. The populations of G. tachinoides showed complete panmixia (FIS = 0, P = 0.5 for the whole sample) and no genetic differentiation among populations or global positioning system trap locations. This is in line with the results of dispersal studies which indicated higher diffusion coefficients for G. tachinoides than for G. p. gambiensis. The impact of these findings is discussed within the framework of control campaigns currently promoted by the Pan African Tsetse and Trypanosomosis Eradication Campaign.

A pilot study to delimit tsetse target populations in Zimbabwe

Background Tsetse (Glossina sensu stricto) are cyclical vectors of human and animal trypanosomoses, that are presently targeted by the Pan African Tsetse and Trypanosomiasis Eradication Campaign (PATTEC) coordinated by the African Union. In order to achieve effective control of tsetse, there is need to produce elaborate plans to guide intervention programmes. A model intended to aid in the planning of intervention programmes and assist a fuller understanding of tsetse distribution was applied, in a pilot study in the Masoka area, Mid-Zambezi valley in Zimbabwe, and targeting two savannah species, Glossina morsitans morsitans and Glossina pallidipes. Methodology/Principal findings The field study was conducted between March and December 2015 in 105 sites following a standardized grid sampling frame. Presence data were used to study habitat suitability of both species based on climatic and environmental data derived from MODIS and SPOT 5 satellite images. Factors influencing distribution were studied using an Ecological Niche Factor Analysis (ENFA) whilst habitat suitability was predicted using a Maximum Entropy (MaxEnt) model at a spatial resolution of 250 m. Area Under the Curve (AUC), an indicator of model performance, was 0.89 for G. m. morsitans and 0.96 for G. pallidipes. We then used the predicted suitable areas to calculate the probability that flies were really absent from the grid cells where they were not captured during the study based on a probability model using a risk threshold of 0.05. Apart from grid cells where G. m. morsitans and G. pallidipes were captured, there was a high probability of presence in an additional 128 km2 and 144 km2 respectively. Conclusions/Significance The modelling process promised to be useful in optimizing the outputs of presence/absence surveys, allowing the definition of tsetse infested areas with improved accuracy. The methodology proposed here can be extended to all the tsetse infested parts of Zimbabwe and may also be useful for other PATTEC national initiatives in other African countries.